pictures of Natural Sources of Heat and Light?

Answer 1

If we look matter at microscopic level, temperature is no other thing that the average molecules or atoms energy due to their random motion.

The fact that temperature is not measured in energy units (Jouls) is only a matter of how historically the measure of temperature was born and, if needed, temperature can be measured in energy units by multiplying the measure in absolute degrees (°K) by a constant called Boltzmann constant.

When a hot piece of matter (that is a piece of matter with fast molecules) is put in contact with a cold piece of matter (that is a piece of matter with slow molecules) collisions between the molecules of the two bodies tends to accelerate the slow molecules and decelerate the fast once. This is seen as cooling the hot body and heating the cold one.

Moreover, particles with a certain energy tends (for a complex quantum mechanical mechanism) to emit light whose frequency is strictly related to the body temperature. As a matter of fact, observing a body emitting light (not reflecting light emitted by another body like objects reflecting sun light) we can deduce its temperature from the color of the emitted light. All the bodies on earth are around 25°C (really in between -30 and 50) and emits in the near infrared. It cannot be seen by eyes, but it can be revealed by infrared glasses (that are generally called night viewers) so that infrared light emitted by objects allows us to use night viewers to see in the absence of sun light.